1. Field of the Invention
The present invention relates to monitoring underground caverns or tunnels, and more particularly, to monitoring underground hydraulic and water quality conditions within various bores extending from and located in close proximity to underground caverns and tunnels.
2. Description of the Prior Art
For the purpose of tunnel construction worker safety and post-construction structural integrity and safety, it is often desirable and required by laws, regulations, etc. to monitor hydraulic changes, which may change rapidly, in saturated fractured rock media and sediments in the earth materials surrounding these underground structures. Additionally, it may be desirable and required by laws, regulations, etc. to monitor groundwater quality within these fractured rock media and sediments. For example, underground caverns and tunnels may exist for a variety of purposes, including the storage of liquefied natural gas (LNG), storage of high level radioactive waste (e.g. spent fuel rods from nuclear power plants), mine shafts and drifts, transportation tunnels, water conduits beneath dams, etc. These caverns and tunnels may become subject to various stresses that could lead to leakage of surrounding fluids into the caverns or tunnels potentially resulting in hydraulic flooding as well as potential collapse due to various stress-related factors.
For example, there are current projects underway wherein large tunnels or caverns are being constructed below ocean floor beds, where surficial benthic sediments of the ocean floor are located at a minimum of 600 feet below ocean water. These tunnels will be used for the storage of liquefied natural gas (LNG). Hydraulic pressure from the overlying ocean water will be used to keep the gas liquefied. Large access tunnels will be constructed to reach each of the LNG tunnels. From these access tunnels, boreholes will be drilled at various angles into the surrounding rock media to monitor changes in hydraulic pressure, which can signal potential leakage of the liquefied natural gas from the storage tunnel. These monitored changes can also signal potential problems with regard to the stabilities within rock media surrounding the access tunnel, thereby indicating a potential need for worker evacuation from the access tunnels. Groundwater that moves through and around the borehole monitoring system from the surrounding rock media will be periodically tested by chemical analysis (e.g. gas chromatography, mass spectroscopy, fiber optical chemical sensor, etc.) in order to monitor LNG leakage from the storage tunnels. LNG that leaks from the storage tunnels will likely change both chemically and physically over a short period of time due to decreasing pressure and differing temperature from an immiscible liquefied phase to a dissolved aqueous phase within the surrounding groundwater fluids. These dissolved gasses can migrate through the processes of hydraulic advection and diffusion through fractured bedrock and permeable sediment to groundwater springs emerging at the ocean floor. These leaks could then dramatically affect aquatic ecology of the surrounding ocean environs and pose significant cost burden for tunnel reparations, as well as translate into replacement costs for the lost LNG. LNG leakage also poses a significant health and safety risk. As an example, dissolved aqueous phase gases can volatilize into gas phase through fractures that intersect access tunnels as well as air spaces inside various groundwater monitoring systems. If there is enough oxygen within these air spaces and pockets, explosive flashes may occur due to electrical spark, welding activity, or even heat generated from cigarette embers. Consequently, it is most critical that all of the monitoring systems throughout these tunnel environments be intrinsically safe.
Generally speaking, to monitor groundwater, boreholes, typically having a length of many hundreds of feet and more, are drilled into the ground so that water in the vicinity of the hole can seep into it. To monitor the water, probes are advanced into the hole to the desired depth where a water sample is taken and transported to the surface. Since water from different borehole depths must not be mixed, to prevent cross contamination, it is necessary to keep water from different borehole depths separate. Keeping waters from different borehole depths separate, and transporting the water to the surface, is difficult, time-consuming and costly.
Current pressure and groundwater monitoring systems are operated sequentially in terms of testing functions such as water quality and pressure. As an example, some of these systems only allow a single port in a multi-level monitoring system to be purged and sampled for groundwater at any one time. Therefore, only one port can be purged and sampled at a time. The sampling device in these systems has to be manually moved from port to port. When it is necessary to record pressure measurements, the water sampling tool must first be removed from the access pipe of the monitoring system, and then the pressure monitoring device installed through the access pipe to then obtain pressure measurements (or vice versa). This exchange of sampling and hydraulic monitoring functions is a typical practice for commercial monitoring systems. Another feature concerning conventional monitoring technologies is that groundwater sampling devices are typically characterized by valve mechanisms that can become easily jammed or clogged with sediment—adding maintenance and repair time and therefore more time and cost for obtaining groundwater samples.
Another disadvantage of conventional groundwater monitoring systems is with respect to the removal rate of “old water” from the system before each sampling event. It is a common practice to remove this old water before each sampling event so that one can be sure that the water being collected is representative of fresh formation water. As an example, some of these systems are constructed with inflatable straddle packer assemblies for isolating sampling and hydraulic monitoring zones. The packers prevent hydraulic cross communication between each sampling port. The volume of groundwater that exists between the packer assemblies is fairly large relative to the water removal rate of these sampling devices that are being used to remove the old water. The problem is exacerbated as the linear distance between the packers becomes greater. The distance between the packers is determined by various factors such as the need to average a water sample over a linear distance or the need to capture the influence of a certain fracture zone(s) between the confines of the packers so that the hydraulic properties of a particular fracture zone can be evaluated without hydraulic interference from other zones.
The conventional sampling technologies that are being used in the commercially available systems consist of sampling vials in one example and miniaturized gas displacement pumps with dual parallel tubing in another case. The sampling vial approach that is typically used consists of 250 ml containers—which can be linked together to make a four-unit interconnected vial chain. However, if the water between the packers is a large volume (e.g. 60 to 90 liters), then removal of the old water could require 60 to 90 trips in and out of the access pipe for a single purge cycle of one straddle packer volume. Given that many of these sampling ports in tunnel systems are deep with respect to ground surface and that numerous time-consuming repetitions of vial entry and removal are required during the purging process, the result is that many hours up to weeks of time may be required for purging a single port. The use of a gas displacement pump with parallel tubing is faster than the vial method in that the pump is lowered into the access pipe only one time for the purge and sampling event for a single port—and therefore avoids the in and out bailing process with sampling vials. However, being that the groundwater access pipes are typically of small diameter, the use of a parallel tube configuration with a gas displacement pump requires that the tubing for the gas-in line and the water return line are very small. Therefore, the amount of water volume storage in the two lines is very small relative to the old water volume stored between each set of straddle packers (or sandpack material surrounding the well bore). This therefore limits the amount of water volume that can be removed with each pump stroke.
With respect to groundwater sampling valve operation, the present invention is very unique in that it is much more forgiving and simple in its valve design than other prior art. Prior art valves that are used in groundwater sampling typically consist of ball valves, poppet valves, double action piston valves, one-way check valves combined with electric impellers or contracting and expanding bladders, and sophisticated mechanical valves that are opened and closed with electronically controlled tubular mechanical arms that dock with the sampling port. These devices are susceptible to plugging from water-borne sediment via intrusion into the sealing mechanisms and mechanical works inside each type of valve. Once sediment has intruded, some of these devices are difficult to clean out and repair, and may require removal of the entire monitoring system to access the impaired valve.
Accordingly, it is desirable to provide a system for monitoring various parameters such as hydraulic pressure (as well as aforementioned parameters such as temperature, eh/pH, etc.) and groundwater quality chemistry at various levels within a borehole that is simpler and more efficient.